Methods for reducing or eliminating α-mannosidase resistant glycans in the production of glycoproteins

ABSTRACT

The present invention provides methods to reduce or eliminate α-mannosidase resistant glycans on glycoproteins in yeast. The reduction or elimination of α-mannosidase resistant glycans on glycoproteins results from the disruption of the newly isolated  P. pastoris  AMR2 gene encoding β1,2-mannosyltransferase. The present invention also discloses novel genes, polypeptides, antibodies, vectors and host cells relating to α-mannosidase resistance on glycans.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/118,008, filed Apr. 29, 2005, now U.S. Pat. No. 7,465,577 and whichclaims benefit of U.S. provisional application Ser. No. 60/620,186 filedon Oct. 18, 2004.

FIELD OF THE INVENTION

The present invention relates to the field of protein glycosylationengineering in lower eukaryotes. The present invention further relatesto engineering of yeast and filamentous fungal host cells for theproduction of therapeutic glycoproteins. In particular, the presentinvention relates to the reduction or elimination of α-mannosidaseresistant glycans on glycoproteins, and methods for reducing oreliminating a gene involved in the production of α-mannosidaseresistance on glycans in yeast cells.

BACKGROUND OF THE INVENTION

The ability to produce recombinant human proteins has led to majoradvances in human health care and remains an active area of drugdiscovery. Many therapeutic proteins require the posttranslationaladdition of glycans to specific asparagine residues (N-glycosylation) ofthe protein to ensure proper structure-function activity and subsequentstability in human serum. For therapeutic use in humans, glycoproteinsrequire human-like N-glycosylation. Mammalian cell lines (e.g., CHOcells, human retinal cells) that can mimic human-like glycoproteinprocessing have several drawbacks including low protein titers, longfermentation times, heterogeneous products, and continued viralcontainment. It is therefore desirable to use an expression system thatnot only produces high protein titers with short fermentation times, butcan also produce human-like glycoproteins.

Fungal hosts such as the methylotrophic yeast Pichia pastoris hasdistinct advantages for therapeutic protein expression—e.g. it does notsecrete high amounts of endogenous proteins, it has a strong induciblepromoter, it can be grown in defined chemical media, and it can producehigh titers of recombinant proteins (Cregg et al., 2000). However,glycosylated proteins expressed in P. pastoris contain additionalmannose sugars resulting in “high mannose” glycans, as well asmannosylphosphate groups which impart a negative charge ontoglycoproteins. Glycoproteins with either high mannose glycans or chargedmannans are a high risk for illiciting an immune response in humans(Takeuchi, 1997; Rosenfeld and Ballou, 1974). Accordingly, it isdesirable to produce therapeutic glycoproteins in fungal host systems,such that the pattern of glycosylation is identical or at least similarto that in humans.

Some fungal hosts contain immunogenic β-mannosylation on glycans ofglycoproteins. In order to circumvent antigenicity, it is desirable toeliminate β-mannosylation in the production of human-like glycoproteins.Oligomannosides with β-1,2-linkage were first described by Shibata etal., (1985) in association with Candida albicans cell wallphosphopeptidomannan by phosphodiester bridges. Subsequently, threetypes of α-1,2 linkages have been identified in the side chains ofCandida cell wall mannans. The first is a β-1,2-linked manno-oligomerlocated in a phosphodiesterified oligosaccharide moiety which is acommon epitope in the mannans of several Candida species (Shibata et al1993a). The second type is a β-1,2-linked mannose unit attached to thenonreducing terminal of the α-1,2 oligomannosyl side chains in themannans of Candida albicans, tropicalis and glabrata (Kobayashi et al.,1989, 1992 and 1994). The third type of β-1,2 linkage is found inCandida guilliermondii and contains β-1,2 linked mannose units attachedto an α-1,3 linked mannose unit (Shibata et al., 1993b).

Despite these findings, the studies on β-1,2 linkages have been limitedby unsuccessful attempts to identify a β-1,2 mannosyl-transferase gene.Suzuki et al., (1997) characterized the presence of aβ-1,2-mannosyltransferase in Candida guilliermondii, however, a gene forthis enzyme has yet to be cloned.

In C. albicans yeast, both the β-oligomannosides which make up theacid-labile region of the phosphomannan complex, and α-oligomannosides,which make up the acid-stable region of the complex, serve as adhesinsin the attachment of these pathogenic yeast cells to host splenic andlymph node macrophages (Cutler, 2001). Interestingly, antibodiesprotective against various forms of candidiasis recognize β-linkedmannotriose, but not oligomannosides of greater mannose chain length(Han et al, 1997). It was reported that patients who develop deep tissueinvasion with C. albicans, do not have detectable antibody titersspecific for β-linked oligomannosides, whereas such antibodies werepresent in healthy individuals (Jouault et al, 1997).

There are few examples of β-linked mannose residues on glycoproteinsfrom P. pastoris. In 1986, Kobayashi et al, described a modifiedacetolysis method with milder conditions for the isolation ofmanno-oligosaccharides composed predominantly of β-1,2 linked mannoseresidues. In 2003, Trimble et al reported the presence of β-1,2-linkedmannose residues in the recombinant human bile salt-stimulated lipase(hBSSL) expressed in P. pastoris. As evidenced by the presence ofprotective antibodies in uninfected individuals, β-linked mannans arelikely to be immunogenic. Additionally, exposed mannose groups ontherapeutic proteins are rapidly cleared by mannose receptors onmacrophage cells, resulting in low drug efficacy. Thus, the presence ofβ-linked mannose residues on N- or O-linked glycans of heterologoustherapeutic proteins expressed in a fungal host e.g., P. pastoris is notdesirable given their immunogenic potential and their ability to bind toclearance factors.

What is needed, therefore, is a method for removing undesired mannoseresidues on glycoproteins for the production of therapeuticglycoproteins.

SUMMARY OF INVENTION

Accordingly, the present invention provides methods for producingglycoprotein compositions in yeast or filamentous fungal host cells,said glycoprotein compositions having reduced amounts of high mannoseglycans, said method comprising reducing or eliminating the presence ofα-mannosidase resistant glycans on said glycoproteins. In certainembodiments, reducing or eliminating α-mannosidase resistant glycans onglycoproteins is accomplished by modifying the host cell throughdisruption, deletion or mutation of a gene involved in mannosylation ofN-glycans. Such genes may include, for example, the gene sequencesdescribed herein as SEQ ID NO: 11 or variants thereof.

In certain embodiments, the α-mannosidase resistant glycans may compriseβ-mannose, branched high mannose, or α-1,4 mannose residues.

The host cells of the present invention are preferably of yeast and/orfilamentous fungal origin. The host cells useful in the presentinvention may include the following families, genie, and species: Pichiapastoris, Pichia finlandica, Pichia trehalophila, Pichia koclamae,Pichia membranaefaciens, Pichia methanolica, Pichia minuta (Ogataeaminuta, Pichia lindneri), Pichia opuntiae, Pichia thermotolerans, Pichisalictaria, Pichia guercum, Pichia pijperi, Pichia stiptis, Pichia sp.,Saccharomyces castellii, Saccharomyces cerevisiae, Saccharomyceskluyveri, Saccharomyces sp., Hansenula polymorpha, Kluyveromyces sp.,Kluyveromyces lactis, Candida albicans, Candida sp., Aspergillusfumigatus, Aspergillus nidulans, Aspergillus niger, Aspergillus oryzae,Trichoderma reesei, Chrysosporium lucknowense, Fusarium sp., Fusariumgramineum, Fusarium venenatum, Physcomitrella patens and Neurosporacrassa.

In certain embodiments, the host cells of the present invention maycomprise a deletion of a functional gene encoding analpha-1,6-mannosyltransferase activity, such as OCH1. In otherembodiments, the host cells of the present invention may furthercomprise a gene encoding an mannosylphosphate transferase activity, suchas PNO1 and MNN4B.

The present invention also provides glycoprotein compositions withreduced amounts of high mannose glycan structures that are recalcitrantto α-mannosidase, which may be produced by the methods of the presentinvention. Such glycoprotein compositions may comprise either N-linkedglycans and/or O-linked glycans.

The present invention further provides isolated nucleic acid sequenceswhich are involved in the production of α-mannosidase resistant glycans.These isolated nucleic acid sequences include the sequences describedherein as SEQ ID NO: 11 or variants thereof. Also included in thepresent invention are other nucleic acid sequences which exhibitstructural similarity to the above sequences. These may include, forexample, degenerate variants of SEQ ID NO: 11 as well as nucleic acidsequences having a high level of nucleotide sequence identity with theabove. Nucleic acid sequences included in the present invention wouldtherefore include those nucleic acid sequences having at least 72% 75%,80% or 85% 90%, 95%, 98%, 99%, 99.9% identity to the sequences of SEQ IDNO: 11 as well as nucleic acid sequences that encode a polypeptidehaving the amino acid sequences which is produced by SEQ ID NO: 11;nucleic acid sequence that encode polypeptides having at least 72% 75%,80% or 85% 90%, 95%, 98%, 99%, 99.9% identity to the polypeptides havingthe amino acid sequences which are produced by SEQ ID NO: 12, SEQ ID NO:13, SEQ ID NO:14, or SEQ ID NO:15; and nucleic acid sequences thathybridize under stringent conditions to the nucleic acid sequencesdescribed as SEQ ID NO: 11. The present invention also includes nucleicacid sequences comprising a fragment of any of the above nucleic acidsequences that is at least 60 contiguous nucleotides in length.

In still other embodiments, the present invention provides modifiedyeast or filamentous fungal host cells. The host cells of the presentinvention may be characterized as having been modified to reduceexpression of the functional gene products of one or more a nucleic acidsequence selected from the group consisting of SEQ ID NO: 11. In certainembodiments, the modified host cell comprises a disruption, deletion ormutation in one or more nucleic acid sequences selected from the groupconsisting of SEQ ID NO: 11. In other embodiments, the modified hostcell comprises a cellular inhibitor of expression of the functional geneproduct of a nucleic acid selected from the group consisting of SEQ IDNO: 11 or variants thereof. Cellular inhibitors of expression useful forthe present invention include, for example antisense DNA and shortinterfering RNA.

In other embodiments, the present invention may comprise modified yeastor filamentous fungal host cells which are capable of expressingglycoprotein compositions having reduced amounts of high mannoseglycans, said glycoprotein compositions comprising reduced presence ofα-mannosidase resistant glycans, for example β-mannosyl residues.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-B depicts the nucleic acid and amino acid sequence of the P.pastoris AMR2 gene.

FIG. 2 A. MALDI-TOF MS showing the N-glycans of P. pastoris YAS137(Δoch1, Δpno1, Δmnn4b). B. MALDI-TOF MS showing the N-glycans of P.pastoris YAS137 after digestion with α-1,2 mannosidase. C. MALDI-TOF MSshowing the N-glycans of P. pastoris PBP130 (Δoch1, Δpno1, Δmnn4b,Δamr2). D. MALDI-TOF MS showing the N-glycans of P. pastoris PBP130(Δoch1, Δpno1, Δmnn4b, Δamr2) after digestion with α-1,2 mannosidase.

FIG. 3 MALDI-TOF MS spectra of the N-glycans of P. pastoris YAS137 afterdigestion with α-1,2 mannosidase and Jack Bean mannosidase.

FIG. 4 illustrates the fusion PCR knock-out strategy of P. pastoris AMR2using the drug resistance marker, kanamycin.

FIG. 5A-E depicts the deduced amino acid sequence of the P. pastorisAMR2 gene and is shown aligned with the amino acid sequence of AMR2homologs from Candida albicans. AMR2p (SEQ ID NO:12), AMR1p (SEQ IDNO:13), AMR3p (SEQ ID NO:14), AMR4p (SEQ ID NO:15), CaORF1 (SEQ IDNO:16), CaORF2 (SEQ ID NO:17), CaORF3 (SEQ ID NO:18), CaORF4 (SEQ IDNO:19), CaORF5 (SEQ ID NO:20), CaORF6 (SEQ ID NO:21), CaORF7 (SEQ IDNO:22), CaORF8 (SEQ ID NO:23).

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise defined herein, scientific and technical terms used inconnection with the present invention shall have the meanings that arecommonly understood by those of ordinary skill in the art. Further,unless otherwise required by context, singular terms shall include theplural and plural terms shall include the singular. Generally,nomenclatures used in connection with, and techniques of biochemistry,enzymology, molecular and cellular biology, microbiology, genetics andprotein and nucleic acid chemistry and hybridization described hereinare those well known and commonly used in the art. The methods andtechniques of the present invention are generally performed according toconventional methods well known in the art and as described in variousgeneral and more specific references that are cited and discussedthroughout the present specification unless otherwise indicated. See,e.g., Sambrook et al. Molecular Cloning: A Laboratory Manual, 2d ed.,Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1989);Ausubel et al., Current Protocols in Molecular Biology, GreenePublishing Associates (1992, and Supplements to 2002); Harlow and Lane,Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory Press,Cold Spring Harbor, N.Y. (1990); Taylor and Drickamer, Introduction toGlycobiology, Oxford Univ. Press (2003); Worthington Enzyme Manual,Worthington Biochemical Corp., Freehold, N.J.; Handbook of Biochemistry:Section A Proteins, Vol I, CRC Press (1976); Handbook of Biochemistry:Section A Proteins, Vol II, CRC Press (1976); Essentials ofGlycobiology, Cold Spring Harbor Laboratory Press (1999).

All publications, patents and other references mentioned herein arehereby incorporated by reference in their entireties.

The following terms, unless otherwise indicated, shall be understood tohave the following meanings:

The term “polynucleotide” or “nucleic acid molecule” refers to apolymeric form of nucleotides of at least 10 bases in length. The termincludes DNA molecules (e.g., cDNA or genomic or synthetic DNA) and RNAmolecules (e.g., mRNA or synthetic RNA), as well as analogs of DNA orRNA containing non-natural nucleotide analogs, non-nativeinternucleoside bonds, or both. The nucleic acid can be in anytopological conformation. For instance, the nucleic acid can besingle-stranded, double-stranded, triple-stranded, quadruplexed,partially double-stranded, branched, hairpinned, circular, or in apadlocked conformation.

Unless otherwise indicated, a “nucleic acid comprising SEQ ID NO:X”refers to a nucleic acid, at least a portion of which has either (i) thesequence of SEQ ID NO:X, or (ii) a sequence complementary to SEQ IDNO:X. The choice between the two is dictated by the context. Forinstance, if the nucleic acid is used as a probe, the choice between thetwo is dictated by the requirement that the probe be complementary tothe desired target.

An “isolated” or “substantially pure” nucleic acid or polynucleotide(e.g., an RNA, DNA or a mixed polymer) is one which is substantiallyseparated from other cellular components that naturally accompany thenative polynucleotide in its natural host cell, e.g., ribosomes,polymerases and genomic sequences with which it is naturally associated.The term embraces a nucleic acid or polynucleotide that (1) has beenremoved from its naturally occurring environment, (2) is not associatedwith all or a portion of a polynucleotide in which the “isolatedpolynucleotide” is found in nature, (3) is operatively linked to apolynucleotide which it is not linked to in nature, or (4) does notoccur in nature. The term “isolated” or “substantially pure” also can beused in reference to recombinant or cloned DNA isolates, chemicallysynthesized polynucleotide analogs, or polynucleotide analogs that arebiologically synthesized by heterologous systems.

However, “isolated” does not necessarily require that the nucleic acidor polynucleotide so described has itself been physically removed fromits native environment. For instance, an endogenous nucleic acidsequence in the genome of an organism is deemed “isolated” herein if aheterologous sequence is placed adjacent to the endogenous nucleic acidsequence, such that the expression of this endogenous nucleic acidsequence is altered. In this context, a heterologous sequence is asequence that is not naturally adjacent to the endogenous nucleic acidsequence, whether or not the heterologous sequence is itself endogenous(originating from the same host cell or progeny thereof) or exogenous(originating from a different host cell or progeny thereof). By way ofexample, a promoter sequence can be substituted (e.g., by homologousrecombination) for the native promoter of a gene in the genome of a hostcell, such that this gene has an altered expression pattern. This genewould now become “isolated” because it is separated from at least someof the sequences that naturally flank it.

A nucleic acid is also considered “isolated” if it contains anymodifications that do not naturally occur to the corresponding nucleicacid in a genome. For instance, an endogenous coding sequence isconsidered “isolated” if it contains an insertion, deletion or a pointmutation introduced artificially, e.g., by human intervention. An“isolated nucleic acid” also includes a nucleic acid integrated into ahost cell chromosome at a heterologous site and a nucleic acid constructpresent as an episome. Moreover, an “isolated nucleic acid” can besubstantially free of other cellular material, or substantially free ofculture medium when produced by recombinant techniques, or substantiallyfree of chemical precursors or other chemicals when chemicallysynthesized.

As used herein, the phrase “degenerate variant” of a reference nucleicacid sequence encompasses nucleic acid sequences that can be translated,according to the standard genetic code, to provide an amino acidsequence identical to that translated from the reference nucleic acidsequence. The term “degenerate oligonucleotide” or “degenerate primer”is used to signify an oligonucleotide capable of hybridizing with targetnucleic acid sequences that are not necessarily identical in sequencebut that are homologous to one another within one or more particularsegments.

The term “percent sequence identity” or “identical” in the context ofnucleic acid sequences refers to the residues in the two sequences whichare the same when aligned for maximum correspondence. The length ofsequence identity comparison may be over a stretch of at least aboutnine nucleotides, usually at least about 20 nucleotides, more usually atleast about 24 nucleotides, typically at least about 28 nucleotides,more typically at least about 32 nucleotides, and preferably at leastabout 36 or more nucleotides. There are a number of different algorithmsknown in the art which can be used to measure nucleotide sequenceidentity. For instance, polynucleotide sequences can be compared usingFASTA, Gap or Bestfit, which are programs in Wisconsin Package Version10.0, Genetics Computer Group (GCG), Madison, Wis. FASTA providesalignments and percent sequence identity of the regions of the bestoverlap between the query and search sequences. Pearson, MethodsEnzymol. 183:63-98 (1990) (hereby incorporated by reference in itsentirety). For instance, percent sequence identity between nucleic acidsequences can be determined using FASTA with its default parameters (aword size of 6 and the NOPAM factor for the scoring matrix) or using Gapwith its default parameters as provided in GCG Version 6.1, hereinincorporated by reference. Alternatively, sequences can be comparedusing the computer program, BLAST (Altschul et al., J. Mol. Biol.215:403-410 (1990); Gish and States, Nature Genet. 3:266-272 (1993);Madden et al., Meth. Enzymol. 266:131-141 (1996); Altschul et al.,Nucleic Acids Res. 25:3389-3402 (1997); Zhang and Madden, Genome Res.7:649-656 (1997)), especially blastp or tblastn (Altschul et al.,Nucleic Acids Res. 25:3389-3402 (1997)).

The term “substantial homology” or “substantial similarity,” whenreferring to a nucleic acid or fragment thereof, indicates that, whenoptimally aligned with appropriate nucleotide insertions or deletionswith another nucleic acid (or its complementary strand), there isnucleotide sequence identity in at least about 50%, more preferably 60%of the nucleotide bases, usually at least about 70%, more usually atleast about 80%, preferably at least about 90%, and more preferably atleast about 95%, 96%, 97%, 98% or 99% of the nucleotide bases, asmeasured by any well-known algorithm of sequence identity, such asFASTA, BLAST or Gap, as discussed above.

Alternatively, substantial homology or similarity exists when a nucleicacid or fragment thereof hybridizes to another nucleic acid, to a strandof another nucleic acid, or to the complementary strand thereof, understringent hybridization conditions. “Stringent hybridization conditions”and “stringent wash conditions” in the context of nucleic acidhybridization experiments depend upon a number of different physicalparameters. Nucleic acid hybridization will be affected by suchconditions as salt concentration, temperature, solvents, the basecomposition of the hybridizing species, length of the complementaryregions, and the number of nucleotide base mismatches between thehybridizing nucleic acids, as will be readily appreciated by thoseskilled in the art. One having ordinary skill in the art knows how tovary these parameters to achieve a particular stringency ofhybridization.

In general, “stringent hybridization” is performed at about 25° C. belowthe thermal melting point (T_(m)) for the specific DNA hybrid under aparticular set of conditions. “Stringent washing” is performed attemperatures about 5° C. lower than the T_(m) for the specific DNAhybrid under a particular set of conditions. The T_(m) is thetemperature at which 50% of the target sequence hybridizes to aperfectly matched probe. See Sambrook et al., Molecular Cloning: ALaboratory Manual, 2d ed., Cold Spring Harbor Laboratory Press, ColdSpring Harbor, N.Y. (1989), page 9.51, hereby incorporated by reference.For purposes herein, “stringent conditions” are defined for solutionphase hybridization as aqueous hybridization (i.e., free of formamide)in 6×SSC (where 20×SSC contains 3.0 M NaCl and 0.3 M sodium citrate), 1%SDS at 65° C. for 8-12 hours, followed by two washes in 0.2×SSC, 0.1%SDS at 65° C. for 20 minutes. It will be appreciated by the skilledworker that hybridization at 65° C. will occur at different ratesdepending on a number of factors including the length and percentidentity of the sequences which are hybridizing.

The nucleic acids (also referred to as polynucleotides) of thisinvention may include both sense and antisense strands of RNA, cDNA,genomic DNA, and synthetic forms and mixed polymers of the above. Theymay be modified chemically or biochemically or may contain non-naturalor derivatized nucleotide bases, as will be readily appreciated by thoseof skill in the art. Such modifications include, for example, labels,methylation, substitution of one or more of the naturally occurringnucleotides with an analog, internucleotide modifications such asuncharged linkages (e.g., methyl phosphonates, phosphotriesters,phosphoramidates, carbamates, etc.), charged linkages (e.g.,phosphorothioates, phosphorodithioates, etc.), pendent moieties (e.g.,polypeptides), intercalators (e.g., acridine, psoralen, etc.),chelators, alkylators, and modified linkages (e.g., alpha anomericnucleic acids, etc.) Also included are synthetic molecules that mimicpolynucleotides in their ability to bind to a designated sequence viahydrogen bonding and other chemical interactions. Such molecules areknown in the art and include, for example, those in which peptidelinkages substitute for phosphate linkages in the backbone of themolecule. Other modifications can include, for example, analogs in whichthe ribose ring contains a bridging moiety or other structure such asthe modifications found in “locked” nucleic acids.

The term “mutated” when applied to nucleic acid sequences means thatnucleotides in a nucleic acid sequence may be inserted, deleted orchanged compared to a reference nucleic acid sequence. A singlealteration may be made at a locus (a point mutation) or multiplenucleotides may be inserted, deleted or changed at a single locus. Inaddition, one or more alterations may be made at any number of lociwithin a nucleic acid sequence. A nucleic acid sequence may be mutatedby any method known in the art including but not limited to mutagenesistechniques such as “error-prone PCR” (a process for performing PCR underconditions where the copying fidelity of the DNA polymerase is low, suchthat a high rate of point mutations is obtained along the entire lengthof the PCR product; see, e.g., Leung et al., Technique, 1:11-15 (1989)and Caldwell and Joyce, PCR Methods Applic. 2:28-33 (1992)); and“oligonucleotide-directed mutagenesis” (a process which enables thegeneration of site-specific mutations in any cloned DNA segment ofinterest; see, e.g., Reidhaar-Olson and Sauer, Science 241:53-57(1988)).

The term “vector” as used herein is intended to refer to a nucleic acidmolecule capable of transporting another nucleic acid to which it hasbeen linked. One type of vector is a “plasmid”, which refers to acircular double stranded DNA loop into which additional DNA segments maybe ligated. Other vectors include cosmids, bacterial artificialchromosomes (BAC) and yeast artificial chromosomes (YAC). Another typeof vector is a viral vector, wherein additional DNA segments may beligated into the viral genome (discussed in more detail below). Certainvectors are capable of autonomous replication in a host cell into whichthey are introduced (e.g., vectors having an origin of replication whichfunctions in the host cell). Other vectors can be integrated into thegenome of a host cell upon introduction into the host cell, and arethereby replicated along with the host genome. Moreover, certainpreferred vectors are capable of directing the expression of genes towhich they are operatively linked. Such vectors are referred to hereinas “recombinant expression vectors” (or simply, “expression vectors”).

As used herein, the term “sequence of interest” or “gene of interest”refers to a nucleic acid sequence, typically encoding a protein that isnot normally produced in the host cell. The methods disclosed hereinallow one or more sequences of interest or genes of interest to beintegrated into a host cell genome. A preferred integration site is theAMR2 locus. Non-limiting examples of sequences of interest includesequences encoding one or more polypeptides having an enzymaticactivity, e.g., an enzyme which affects N-glycan synthesis in a hostsuch as mannosyltransferases, N-acetylglucosaminyltransferases,UDP-N-acetylglucosamine transporters, galactosyltransferases andsialyltransferases.

As used herein, the term “therapeutic glycoprotein” includeserythropoietin, cytokines such as interferon-α, interferon-β,interferon-γ, interferon-ω, and granulocyte-CSF, GM-CSF, coagulationfactors such as factor VIII, factor IX, and human protein C,antithrombin III, thrombin, soluble IgE receptor α-chain, IgG, IgGfragments, IgG fusions, IgM, interleukins, urokinase, chymase, and ureatrypsin inhibitor, IGF-binding protein, epidermal growth factor, growthhormone-releasing factor, annexin V fusion protein, angiostatin,vascular endothelial growth factor-2, myeloid progenitor inhibitoryfactor-1, osteoprotegerin, α-1-antitrypsin, α-feto proteins, DNase II,kringle 3 of human plasminogen, glucocerebrosidase, TNF binding protein1, follicle stimulating hormone, cytotoxic T lymphocyte associatedantigen 4-Ig, transmembrane activator and calcium modulator andcyclophilin ligand, soluble TNF receptor Fc fusion, glucagon-likeprotein 1, IL-2 receptor agonist.

“Operatively linked” expression control sequences refers to a linkage inwhich the expression control sequence is contiguous with the gene ofinterest to control the gene of interest, as well as expression controlsequences that act in trans or at a distance to control the gene ofinterest.

The term “expression control sequence” as used herein refers topolynucleotide sequences which are necessary to affect the expression ofcoding sequences to which they are operatively linked. Expressioncontrol sequences are sequences which control the transcription,post-transcriptional events and translation of nucleic acid sequences.Expression control sequences include appropriate transcriptioninitiation, termination, promoter and enhancer sequences; efficient RNAprocessing signals such as splicing and polyadenylation signals;sequences that stabilize cytoplasmic mRNA; sequences that enhancetranslation efficiency (e.g., ribosome binding sites); sequences thatenhance protein stability; and when desired, sequences that enhanceprotein secretion. The nature of such control sequences differsdepending upon the host organism; in prokaryotes, such control sequencesgenerally include promoter, ribosomal binding site, and transcriptiontermination sequence. The term “control sequences” is intended toinclude, at a minimum, all components whose presence is essential forexpression, and can also include additional components whose presence isadvantageous, for example, leader sequences and fusion partnersequences.

The term “recombinant host cell” (or simply “host cell”), as usedherein, is intended to refer to a cell into which a recombinant vectorhas been introduced. It should be understood that such terms areintended to refer not only to the particular subject cell but to theprogeny of such a cell. Because certain modifications may occur insucceeding generations due to either mutation or environmentalinfluences, such progeny may not, in fact, be identical to the parentcell, but are still included within the scope of the term “host cell” asused herein. A recombinant host cell may be an isolated cell or cellline grown in culture or may be a cell which resides in a living tissueor organism.

The term “peptide” as used herein refers to a short polypeptide, e.g.,one that is typically less than about 50 amino acids long and moretypically less than about 30 amino acids long. The term as used hereinencompasses analogs and mimetics that mimic structural and thusbiological function.

The term “polypeptide” encompasses both naturally-occurring andnon-naturally-occurring proteins, and fragments, mutants, derivativesand analogs thereof. A polypeptide may be monomeric or polymeric.Further, a polypeptide may comprise a number of different domains eachof which has one or more distinct activities. The term “isolatedprotein” or “isolated polypeptide” is a protein or polypeptide that byvirtue of its origin or source of derivation (1) is not associated withnaturally associated components that accompany it in its native state,(2) exists in a purity not found in nature, where purity can be adjudgedwith respect to the presence of other cellular material (e.g., is freeof other proteins from the same species) (3) is expressed by a cell froma different species, or (4) does not occur in nature (e.g., it is afragment of a polypeptide found in nature or it includes amino acidanalogs or derivatives not found in nature or linkages other thanstandard peptide bonds). Thus, a polypeptide that is chemicallysynthesized or synthesized in a cellular system different from the cellfrom which it naturally originates will be “isolated” from its naturallyassociated components. A polypeptide or protein may also be renderedsubstantially free of naturally associated components by isolation,using protein purification techniques well known in the art. As thusdefined, “isolated” does not necessarily require that the protein,polypeptide, peptide or oligopeptide so described has been physicallyremoved from its native environment.

The term “polypeptide fragment” as used herein refers to a polypeptidethat has a deletion, e.g., an amino-terminal and/or carboxy-terminaldeletion compared to a full-length polypeptide. In a preferredembodiment, the polypeptide fragment is a contiguous sequence in whichthe amino acid sequence of the fragment is identical to thecorresponding positions in the naturally-occurring sequence. Fragmentstypically are at least 5, 6, 7, 8, 9 or 10 amino acids long, preferablyat least 12, 14, 16 or 18 amino acids long, more preferably at least 20amino acids long, more preferably at least 25, 30, 35, 40 or 45, aminoacids, even more preferably at least 50 or 60 amino acids long, and evenmore preferably at least 70 amino acids long.

A “modified derivative” refers to polypeptides or fragments thereof thatare substantially homologous in primary structural sequence but whichinclude, e.g., in vivo or in vitro chemical and biochemicalmodifications or which incorporate amino acids that are not found in thenative polypeptide. Such modifications include, for example,acetylation, carboxylation, phosphorylation, glycosylation,ubiquitination, labeling, e.g., with radionuclides, and variousenzymatic modifications, as will be readily appreciated by those skilledin the art. A variety of methods for labeling polypeptides and ofsubstituents or labels useful for such purposes are well known in theart, and include radioactive isotopes such as ¹²⁵I, ³²P, ³⁵S, and ³H,ligands which bind to labeled antiligands (e.g., antibodies),fluorophores, chemiluminescent agents, enzymes, and antiligands whichcan serve as specific binding pair members for a labeled ligand. Thechoice of label depends on the sensitivity required, ease of conjugationwith the primer, stability requirements, and available instrumentation.Methods for labeling polypeptides are well known in the art. See, e.g.,Ausubel et al., Current Protocols in Molecular Biology, GreenePublishing Associates (1992, and Supplements to 2002) (herebyincorporated by reference).

The term “fusion protein” refers to a polypeptide comprising apolypeptide or fragment coupled to heterologous amino acid sequences.Fusion proteins are useful because they can be constructed to containtwo or more desired functional elements from two or more differentproteins. A fusion protein comprises at least 10 contiguous amino acidsfrom a polypeptide of interest, more preferably at least 20 or 30 aminoacids, even more preferably at least 40, 50 or 60 amino acids, yet morepreferably at least 75, 100 or 125 amino acids. Fusions that include theentirety of the proteins of the present invention have particularutility. The heterologous polypeptide included within the fusion proteinof the present invention is at least 6 amino acids in length, often atleast 8 amino acids in length, and usefully at least 15, 20, and 25amino acids in length. Fusions that include larger polypeptides, such asan IgG Fc region, and even entire proteins, such as the greenfluorescent protein (“GFP”) chromophore-containing proteins, haveparticular utility. Fusion proteins can be produced recombinantly byconstructing a nucleic acid sequence which encodes the polypeptide or afragment thereof in frame with a nucleic acid sequence encoding adifferent protein or peptide and then expressing the fusion protein.Alternatively, a fusion protein can be produced chemically bycrosslinking the polypeptide or a fragment thereof to another protein.

As used herein, the term “antibody” refers to a polypeptide, at least aportion of which is encoded by at least one immunoglobulin gene, orfragment thereof, and that can bind specifically to a desired targetmolecule. The term includes naturally-occurring forms, as well asfragments and derivatives.

Fragments within the scope of the term “antibody” include those producedby digestion with various proteases, those produced by chemical cleavageand/or chemical dissociation and those produced recombinantly, so longas the fragment remains capable of specific binding to a targetmolecule. Among such fragments are Fab, Fab′, Fv, F(ab′)₂, and singlechain Fv (scFv) fragments.

Derivatives within the scope of the term include antibodies (orfragments thereof) that have been modified in sequence, but remaincapable of specific binding to a target molecule, including:interspecies chimeric and humanized antibodies; antibody fusions;heteromeric antibody complexes and antibody fusions, such as diabodies(bispecific antibodies), single-chain diabodies, and intrabodies (see,e.g., Intracellular Antibodies: Research and Disease Applications,(Marasco, ed., Springer-Verlag New York, Inc., 1998), the disclosure ofwhich is incorporated herein by reference in its entirety).

As used herein, antibodies can be produced by any known technique,including harvest from cell culture of native B lymphocytes, harvestfrom culture of hybridomas, recombinant expression systems and phagedisplay.

The term “non-peptide analog” refers to a compound with properties thatare analogous to those of a reference polypeptide. A non-peptidecompound may also be termed a “peptide mimetic” or a “peptidomimetic”.See, e.g., Jones, Amino Acid and Peptide Synthesis, Oxford UniversityPress (1992); Jung, Combinatorial Peptide and Nonpeptide Libraries: AHandbook, John Wiley (1997); Bodanszky et al., Peptide Chemistry—APractical Textbook, Springer Verlag (1993); Synthetic Peptides: A UsersGuide, (Grant, ed., W. H. Freeman and Co., 1992); Evans et al., J. Med.Chem. 30:1229 (1987); Fauchere, J. Adv. Drug Res. 15:29 (1986); Veberand Freidinger, Trends Neurosci., 8:392-396 (1985); and references sitedin each of the above, which are incorporated herein by reference. Suchcompounds are often developed with the aid of computerized molecularmodeling. Peptide mimetics that are structurally similar to usefulpeptides of the invention may be used to produce an equivalent effectand are therefore envisioned to be part of the invention.

A “polypeptide mutant” or “mutein” refers to a polypeptide whosesequence contains an insertion, duplication, deletion, rearrangement orsubstitution of one or more amino acids compared to the amino acidsequence of a native or wild-type protein. A mutein may have one or moreamino acid point substitutions, in which a single amino acid at aposition has been changed to another amino acid, one or more insertionsand/or deletions, in which one or more amino acids are inserted ordeleted, respectively, in the sequence of the naturally-occurringprotein, and/or truncations of the amino acid sequence at either or boththe amino or carboxy termini. A mutein may have the same but preferablyhas a different biological activity compared to the naturally-occurringprotein.

A mutein has at least 65% overall sequence homology to its wild-typecounterpart. Even more preferred are muteins having at least 70%, 75%,80%, 85% or 90% overall sequence homology to the wild-type protein. Inan even more preferred embodiment, a mutein exhibits at least 95%sequence identity, even more preferably 98%, even more preferably 99%and even more preferably 99.9% overall sequence identity. Sequencehomology may be measured by any common sequence analysis algorithm, suchas Gap or Bestfit.

Amino acid substitutions can include those which: (1) reducesusceptibility to proteolysis, (2) reduce susceptibility to oxidation,(3) alter binding affinity for forming protein complexes, (4) alterbinding affinity or enzymatic activity, and (5) confer or modify otherphysicochemical or functional properties of such analogs.

As used herein, the twenty conventional amino acids and theirabbreviations follow conventional usage. See Immunology—A Synthesis(Golub and Gren eds., Sinauer Associates, Sunderland, Mass., 2^(nd) ed.1991), which is incorporated herein by reference. Stereoisomers (e.g.,D-amino acids) of the twenty conventional amino acids, unnatural aminoacids such as α-, α-disubstituted amino acids, N-alkyl amino acids, andother unconventional amino acids may also be suitable components forpolypeptides of the present invention. Examples of unconventional aminoacids include: 4-hydroxyproline, γ-carboxyglutamate,ε-N,N,N-trimethyllysine, ε-N-acetyllysine, O-phosphoserine,N-acetylserine, N-formylmethionine, 3-methylhistidine, 5-hydroxylysine,N-methylarginine, and other similar amino acids and imino acids (e.g.,4-hydroxyproline). In the polypeptide notation used herein, theleft-hand end corresponds to the amino terminal end and the right-handend corresponds to the carboxy-terminal end, in accordance with standardusage and convention.

A protein has “homology” or is “homologous” to a second protein if thenucleic acid sequence that encodes the protein has a similar sequence tothe nucleic acid sequence that encodes the second protein.Alternatively, a protein has homology to a second protein if the twoproteins have “similar” amino acid sequences. (Thus, the term“homologous proteins” is defined to mean that the two proteins havesimilar amino acid sequences.) In a preferred embodiment, a homologousprotein is one that exhibits at least 72% sequence homology to the wildtype protein, more preferred is at least 75% sequence homology. Evenmore preferred are homologous proteins that exhibit at least 80%, 85%,90% or 95% sequence homology to the wild type protein. In a yet morepreferred embodiment, a homologous protein exhibits at least 96%, 98%,99% or 99.9% sequence identity. As used herein, homology between tworegions of amino acid sequence (especially with respect to predictedstructural similarities) is interpreted as implying similarity infunction.

When “homologous” is used in reference to proteins or peptides, it isrecognized that residue positions that are not identical often differ byconservative amino acid substitutions. A “conservative amino acidsubstitution” is one in which an amino acid residue is substituted byanother amino acid residue having a side chain (R group) with similarchemical properties (e.g., charge or hydrophobicity). In general, aconservative amino acid substitution will not substantially change thefunctional properties of a protein. In cases where two or more aminoacid sequences differ from each other by conservative substitutions, thepercent sequence identity or degree of homology may be adjusted upwardsto correct for the conservative nature of the substitution. Means formaking this adjustment are well known to those of skill in the art. See,e.g., Pearson, 1994, Methods Mol. Biol. 24:307-31 and 25:365-89 (hereinincorporated by reference).

The following six groups each contain amino acids that are conservativesubstitutions for one another: 1) Serine (S), Threonine (T); 2) AsparticAcid (D), Glutamic Acid (E); 3) Asparagine (N), Glutamine (Q); 4)Arginine (R), Lysine (K); 5) Isoleucine (I), Leucine (L), Methionine(M), Alanine (A), Valine (V), and 6) Phenylalanine (F), Tyrosine (Y),Tryptophan (W).

Sequence homology for polypeptides, which is also referred to as percentsequence identity, is typically measured using sequence analysissoftware. See, e.g., the Sequence Analysis Software Package of theGenetics Computer Group (GCG), University of Wisconsin BiotechnologyCenter, 910 University Avenue, Madison, Wis. 53705. Protein analysissoftware matches similar sequences using a measure of homology assignedto various substitutions, deletions and other modifications, includingconservative amino acid substitutions. For instance, GCG containsprograms such as “Gap” and “Bestfit” which can be used with defaultparameters to determine sequence homology or sequence identity betweenclosely related polypeptides, such as homologous polypeptides fromdifferent species of organisms or between a wild-type protein and amutein thereof. See, e.g., GCG Version 6.1.

A preferred algorithm when comparing a particular polypeptide sequenceto a database containing a large number of sequences from differentorganisms is the computer program BLAST (Altschul et al., J. Mol. Biol.215:403-410 (1990); Gish and States, Nature Genet. 3:266-272 (1993);Madden et al., Meth. Enzymol. 266:131-141 (1996); Altschul et al.,Nucleic Acids Res. 25:3389-3402 (1997); Zhang and Madden, Genome Res.7:649-656 (1997)), especially blastp or tblastn (Altschul et al.,Nucleic Acids Res. 25:3389-3402 (1997)).

Preferred parameters for BLASTp are:

Expectation value: 10 (default); Filter: seg (default); Cost to open agap: 11 (default); Cost to extend a gap: 1 (default); Max. alignments:100 (default); Word size: 11 (default); No. of descriptions: 100(default); Penalty Matrix: BLOWSUM62.

The length of polypeptide sequences compared for homology will generallybe at least about 16 amino acid residues, usually at least about 20residues, more usually at least about 24 residues, typically at leastabout 28 residues, and preferably more than about 35 residues. Whensearching a database containing sequences from a large number ofdifferent organisms, it is preferable to compare amino acid sequences.Database searching using amino acid sequences can be measured byalgorithms other than blastp known in the art. For instance, polypeptidesequences can be compared using FASTA, a program in GCG Version 6.1.FASTA provides alignments and percent sequence identity of the regionsof the best overlap between the query and search sequences. Pearson,Methods Enzymol. 183:63-98 (1990) (herein incorporated by reference).For example, percent sequence identity between amino acid sequences canbe determined using FASTA with its default parameters (a word size of 2and the PAM250 scoring matrix), as provided in GCG Version 6.1, hereinincorporated by reference.

“Specific binding” refers to the ability of two molecules to bind toeach other in preference to binding to other molecules in theenvironment. Typically, “specific binding” discriminates overadventitious binding in a reaction by at least two-fold, more typicallyby at least 10-fold, often at least 100-fold. Typically, the affinity oravidity of a specific binding reaction, as quantified by a dissociationconstant, is about 10⁻⁷ M or stronger (e.g., about 10⁻⁸ M, 10⁻⁹ M oreven stronger).

The term “region” as used herein refers to a physically contiguousportion of the primary structure of a biomolecule. In the case ofproteins, a region is defined by a contiguous portion of the amino acidsequence of that protein.

The term “domain” as used herein refers to a structure of a biomoleculethat contributes to a known or suspected function of the biomolecule.Domains may be co-extensive with regions or portions thereof; domainsmay also include distinct, non-contiguous regions of a biomolecule.Examples of protein domains include, but are not limited to, an Igdomain, an extracellular domain, a transmembrane domain, and acytoplasmic domain.

As used herein, the term “molecule” means any compound, including, butnot limited to, a small molecule, peptide, protein, sugar, nucleotide,nucleic acid, lipid, etc., and such a compound can be natural orsynthetic.

The term “high mannose” as used herein refers to a glycan structure on aglycoprotein which is natively produced by species of yeast and/orfilamentous fungi, and generally has eight or more mannose residues.

As used herein, the term “molecule” means any compound, including, butnot limited to, a small molecule, peptide, protein, sugar, nucleotide,nucleic acid, lipid, etc., and such a compound can be natural orsynthetic.

The terms “α-mannosidase resistant glycans” and “recalcitrant α-mannoseglycans” are used interchangeably herein and refer to glycan structureof a glycoprotein which are wholly or partially resistant to cleavage byalpha-mannosidases, such as with α-1,2; α-1,3; and/orα-1,6-mannosidases. Recalcitrant α-mannose glycans may includeβ-mannose, branched high mannose, α-1,4 mannose or uncharacterizedmannose. These glycan structures therefore contribute to increasedpresence of high mannose glycan structures.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention pertains. Exemplary methods andmaterials are described below, although methods and materials similar orequivalent to those described herein can also be used in the practice ofthe present invention and will be apparent to those of skill in the art.All publications and other references mentioned herein are incorporatedby reference in their entirety. In case of conflict, the presentspecification, including definitions, will control. The materials,methods, and examples are illustrative only and not intended to belimiting.

Throughout this specification and claims, the word “comprise” orvariations such as “comprises” or “comprising”, will be understood toimply the inclusion of a stated integer or group of integers but not theexclusion of any other integer or group of integers.

Identification of α-Mannosidase Resistant Gene

In an effort to express human-like glycoproteins in fungal systems,elimination of non-human glycosylation is desired. Fungal glycosylationis characterized by high mannose/non-human glycans. Determining the typeof mannosylation is commonly the first step in eliminating undesiredglycosylation events. The deletion of OCH1 in P. pastoris led to adecrease in hypermannosylation (Choi et al., 2003). Analysis by negativeMALDI-TOF MS, revealed the presence of negative charges associated withthese mannose groups. The subsequent deletion of the putativemannosylphosphate transferase genes, PNO1 and MNN4B, led to a straindevoid of mannosylphosphate (FIG. 2A) (U.S. Pat. No. 7,259,007).Digestion of the remaining mannose groups by α-1,2 mannosidase and JackBean mannosidase further reduced the size of the mannans (FIG. 2B, FIG.3) (Example 1). Despite these gene disruptions and digests withα-mannosidases, up to 20% of the N-glycans remained resistant. Fromsugar composition analysis, and the resistance of these mannose groupsto α-1,2 mannosidase and Jack Bean mannosidase (α-1,2/α-1,3/α-1,6) itwas deduced that these mannose structures are branched β-mannose, highmannose, α-1,4 mannose or uncharacterized mannose.

It was initially postulated that these resistant mannans result frommannosyltransferase activity, and it was thus speculated that the gene(or genes) responsible for these resistant mannans would have somehomology to other mannosyltransferase genes. A C-terminal sequence fromthe Saccharomyces cerevisiae MNN4 gene was used to probe the P. pastorisgenome (Example 2). By selecting genes encoding putative Type IImembrane proteins (and thus, could be found on the Golgi membrane), agene was identified that when disrupted, eliminates the resistantmannans after digest with α-1,2 mannosidase (FIG. 2D). We have namedthis gene AMR2 (alpha-mannosidase resistant). Accordingly, the presentinvention discloses a P. pastoris gene involved in mannosylation ofglycoproteins as set forth in FIG. 1.

Nucleic Acid Sequences

In one aspect of the present invention, a gene involved in themannosylation of N-glycans which are resistant to known α-mannosidasesis identified and sequenced in P. pastoris (FIG. 1, Example 2). In oneembodiment, a nucleic acid sequence encoding the P. pastoris AMR2 geneand variants thereof are provided. Disruption of the P. pastoris AMR2gene is particularly useful for the reduction or elimination ofα-mannosidase-resistant glycans on glycoproteins in a yeast strain. Inanother embodiment, the present invention provides a nucleic acidmolecule comprising or consisting of a sequence which is a variant ofthe P. pastoris AMR2 gene having at least 72% identity to SEQ ID NO: 11.The nucleic acid sequence preferably has at least 75%, 80% or 85%identity to the wild type gene. Even more preferably, the nucleic acidsequence has 90%, 95%, 98%, 99%, 99.9% or even higher identity to theSEQ ID NO: 11.

According to other embodiments of the invention, the nucleic acidmolecule of the invention encodes a polypeptide having the amino acidsequence shown in FIG. 1. Also provided is a nucleic acid moleculeencoding a polypeptide sequence that is at least 72% identical to SEQ IDNO: 12. Typically, the nucleic acid molecule of the invention encodes apolypeptide sequence of at least 75%, 80% or 85% identity to SEQ ID NO:12. Even more preferably, the encoded polypeptide has 90%, 95%, 98%,99%, 99.9% or even higher identity to the SEQ ID NO: 12.

In another aspect of the invention, the AMR2 gene involved inα-mannosidase-resistant mannosylation of N-glycans is homologous tothree other genes in P. pastoris-AMR1, AMR3, AMR4 (FIG. 5), and hasregions of homology to genes in the following species: eleven genes inCandida albicans, (eight shown in FIG. 5); eight genes in Saccharomycescastellii strain NRRL Y-12630; two genes in Saccharomyces kluyveristrain NRRL Y-12651, and three genes in Aspergillus fumigatus (Example3). For the reduction or elimination of recalcitrant α-mannose glycansin other species, a person skilled in the art can identify AMR2 homologsfrom the genome of a given species, and disrupt the homologous gene orgenes. One skilled in the art understands that it may be necessary todisrupt all homologous genes, or a combination of homologous genes foundin any given species. More specifically, a skilled artisan recognizesthat in order to reduce or eliminate α-mannosidase resistant N-glycansin other species, degenerate primers from the conserved sequences can bedesigned for PCR cloning of AMR2 homologs. Alternatively a probe couldalso be constructed for hybridization of the AMR2 homologs.

Host Cells

In another aspect of the invention, a host cell producing glycoproteins,which normally has α-mannosidase-resistant glycans, has been engineeredto produce glycoproteins without α-mannosidase-resistant N-glycans. Inone embodiment, a host cell producing therapeutic glycoproteins, whichnormally has mannosidase-resistant glycans, has been engineered toproduce therapeutic glycoproteins without mannosidase-resistant glycans.In a preferred embodiment, the host cells of the invention have beenmutated by recombination with a disruption, deletion or mutation of theisolated nucleic acid of the invention so that the α-mannosylation onglycans in the host cell is reduced compared to a host cell lacking themutation. More preferably, α-mannosidase-resistance on N-glycans iseliminated. The host cell of the invention is preferably Pichia pastorisor Pichia methanolica, but other host cells, especially yeast cells, arealso encompassed within the scope of the invention.

In some embodiments, the AMR2 gene in a yeast host cell is disrupted bythe PCR knock-out strategy discussed in Example 3 and shown in FIG. 4.In other embodiments of the invention, host cells defective inα-mannosidase resistance activity are used to integrate one or moresequences or genes of interest into the host cell genome using nucleicacid molecules and/or methods of the invention. In a preferredembodiment, the sequences or genes of interest are integrated so as todisrupt an endogenous gene of the host cell. For example, the AMR2 geneis disrupted by a sequence of interest. Host cells containing theintegration are easily identified by a selection marker, which in yeastare usually auxotrophic genes that allow growth of transformed cells ona medium lacking the specific amino acid or nucleotide or an antibioticresistance gene, which allows for growth on media containing thecorresponding antibiotic.

In another aspect of the invention, host cells transformed with thenucleic acid molecules or vectors of the invention, and descendantsthereof, are provided. In some embodiments of the invention, these cellscarry the nucleic acid sequences of the invention on vectors, which maybut need not be freely replicating vectors. In other embodiments of theinvention, the nucleic acids have been integrated into the genome of thehost cells.

The disrupted AMR2 gene which encodes an activity involved in α-mannoseresistance on glycans of glycoproteins is preferably from a yeast strainbelonging to the genus Pichia. Yeasts belonging to the genus Pichiaaccording to the present invention include for example, Pichia pastoris,Pichia finlandica, Pichia trehalophila, Pichia koclamae, Pichiamembranaefaciens, Pichia methanolica, Pichia minuta (Ogataea minuta,Pichia lindneri), Pichia opuntiae, Pichia thermotolerans, Pichisalictaria, Pichia guercum, Pichia pijperi, Pichia stiptis, Pichia sp.,and other yeasts, but not limited thereto. In yet another embodiment,genes carrying AMR2 activity and/or homology can be disrupted in one ofthe following hosts: Saccharomyces castellii, Saccharomyces cerevisiae,Saccharomyces kluyveri, Saccharomyces sp., Hansenula polymorpha,Kluyveromyces sp., Kluyveromyces lactis, Candida albicans, Candida sp.,Aspergillus fumigatus, Aspergillus nidulans, Aspergillus niger,Aspergillus oryzae, Trichoderma reesei, Chrysosporium lucknowense,Fusarium sp., Fusarium gramineum, Fusarium venenatum, Physcomitrellapatens and Neurospora crassa.

AMR2 Gene Encoding β-Mannosylation Activity

It was observed that some yeast species with homologs to this AMR2 genealso have α-mannosylation activity. Accordingly, in another aspect ofthe invention, the AMR2 gene encodes β-mannosyltransferase activity. Inone embodiment, AMR2 encoding β-mannosyltransferase activity isdisrupted individually and/or in combination with any of its homologs inP. pastoris or other fungal species, resulting in the reduction orelimination of α-mannosylation resistant glycans on glycoproteins.

The presence of β-mannosylation on O-glycans is discussed in the reportby Trimble et al, 2003. Accordingly, in a further embodiment,α-mannosidase resistant O-glycans in P. pastoris and other species isreduced or eliminated with the disruption of the AMR2 gene and itshomologs.

The following are examples which illustrate the compositions and methodsof this invention. These examples should not be construed aslimiting—the examples are included for the purposes of illustrationonly.

Example 1 Jack Bean and α-1,2 Mannosidase Digestion of N-Glycans

The standard N-linked oligosaccharides (20 μg) was reconstituted in 100μl HPLC grade water. A 10 μl aliquot was added to a 0.6 ml siliconizedtube. The sample was evaporated to dryness. To the sample, 10 μl of 50mM ammonium acetate was added, along with Jack Bean mannosidase (0.03U)or α-1,2 mannosidase from Trichoderma reseei (0.03 mU, a gift from DrContreras R, Unit of Fundamental and Applied Molecular Biology,Department of Molecular Biology, Ghent University, Ghent, Belgium). Thesample was incubated with the enzyme for 16 to 24 hr at 37° C. Thesample was then evaporated to dryness. The sample was reconstituted in10 μl of water. The sample was subsequently analyzed by MALDI-TOF MS.

Matrix Assisted Laser Desorption Ionization Time of Flight MassSpectrometry

Molecular weights of the glycans were determined using a Voyager DE PROlinear MALDI-TOF (Applied Biosciences) mass spectrometer using delayedextraction. The dried glycans from each well were dissolved in 15 uL ofwater and 0.5 uL spotted on stainless steel sample plates and mixed with0.5 uL of S-DHB matrix (9 mg/mL of dihydroxybenzoic acid, 1 mg/mL of5-methoxysalicilic acid in 1:1 water/acetonitrile 0.1% TFA) and allowedto dry.

Ions were generated by irradiation with a pulsed nitrogen laser (337 nm)with a 4 ns pulse time. The instrument was operated in the delayedextraction mode with a 125 ns delay and an accelerating voltage of 20kV. The grid voltage was 93.00%, guide wire voltage was 0.10%, theinternal pressure was less than 5×10-7 torr, and the low mass gate was875 Da. Spectra were generated from the sum of 100-200 laser pulses andacquired with a 2 GHz digitizer. Man₅GlcNAc₂ oligosaccharide was used asan external molecular weight standard. All spectra were generated withthe instrument in the positive ion mode. The estimated mass accuracy ofthe spectra was 0.5%.

Example 2 Identification and Sequence Analysis of AMR2 Gene from Pichiapastoris

The C-terminal part of Saccharomyces cerevisiae MNN4 gene (Genbankaccession # P36044) containing a repetitive sequence rich in lysine andglutamic acid was used as a probe to blast against a P. pastoris genomicsequence (Integrated Genomics, Chicago, Ill.). Several DNA fragmentswith ORF's encoding proteins with similar lysine and glutamic acid richrepeats were identified. Among those one ORF was found to encode for aprotein of 644 amino acids with putative N-terminal transmembrane domainand C-terminal tail rich in lysine and glutamic acid structurallyresembling S. cerevisiae Mnn4p. Base on the phenotype analysis of thestrain carrying mutated allele, the gene was named AMR2(alpha-mannosidase resistant). Subsequent blast searches of P. pastorisgenomic sequence revealed the presence of three more genes closelyrelated to AMR2.

Example 3 Deletion of AMR2 Gene in YAS137 Strain

P. pastoris strain YAS137 (Δoch1, Δpno1, Δmnn4b) (U.S. Pat. No.7,259,007) was used as a host for the AMR2 gene knockout experiment.YAS137 produces charge free N-glycans without outer chain (FIG. 2A).When digested with α-1,2-mannosidase (FIG. 2B) and Jack Bean (withα-1,2/α-1,3/α-1,6 activity) mannosidases, a significant percentage ofN-glycans purified from strain YAS137 can be converted to Man₅GlcNAc₂.However, up to 20% of the total N-glycans are recalcitrant to theseα-mannosidases (FIG. 3). The amr2 deletion allele (amr2::Kan^(R)) wasgenerated by the PCR overlap method (FIG. 4). Primers PBS1-2-C3 (SEQ IDNO: 1) (5′-TAATAGTGGAGAAA-CTTGCAAAGG-3′) paired with PBS2-KO2 (SEQ IDNO: 2) (5′-GTGCTACCTAAAT-CGTATGTGTCGTTGAAGCTTCCCAATGATAGC-3′), andPBS1-2-KO3 (SEQ ID NO: 3)(5′-CTCCCTATAGTGAGTCGTATTCATATGAT-GGGTGTTTGCTCACTC-3′) paired withPBS1-2-KO4 (SEQ ID NO: 4) (5′-CTTGG-TTCAACGCAGCACTTTG-AC-3′) were usedto amplify the 5′ and 3′ flanking regions of the AMR2 gene from genomicDNA (genomic DNA was isolated from strain NRRL-Y11430). Primers PR29(SEQ ID NO: 5) (5′-CACATACGATTTAG-GTGACAC-3′) paired with PR32 (SEQ IDNO: 6) (5′-AATACGACTCACTATAGG-GAG-3′) were used to amplify the Kan(G418) resistance marker from vector pUG6 (Goldstein and McCusker,1999). Subsequently, primers PBS1-2-C3 and PBS1-2-KO4 were used in asecond reaction with all three products from the first round of PCRreactions to generate an overlap product. The resulting fusion PCRproduct was used to transform strain YAS137. DNA for transformation wasprepared by adding sodium acetate to a final concentration of 0.3 M. Onehundred percent ice-cold ethanol was then added to a final concentrationof 70% to the DNA sample. DNA was pelleted by centrifugation (12000 g×10min) and washed twice with 70% ice-cold ethanol. The DNA was dried andthen resuspended in 50 μl of 10 mM Tris, pH 8.0. YAS137 was prepared byexpanding a yeast culture in BMGY (buffered minimal glycerol: 100 mMpotassium phosphate, pH 6.0; 1.34% yeast nitrogen base; 4×10⁻⁵% biotin;1% glycerol) to an O.D. of ˜2-6. The yeast were made electrocompetent bywashing 3 times in 1M sorbitol and resuspending in 1-2 mls 1M sorbitol.DNA (1-2 μg) was mixed with 50 μl of competent yeast and incubated onice for 1 min. Yeast were then electroporated with a BTX ElectrocellManipulator 600 using the following parameters: 1.5 kV, 129 ohms, and 25μF. One milliliter of YPDS (1% yeast extract, 2% peptone, 2% dextrose,1M sorbitol) was added to the electroporated cells. Transformed yeastwas subsequently plated on selective agar plates. Transformants wereselected on YPD medium containing 200 μg/ml of G418 sulfate, GIBCO™.Proper integration of deletion allele amr2::Kan^(R) was confirmed byPCR. Screening for knockouts was performed by PCR amplification of boththe 5′ and 3′ portions of the knockout construct. PBS1-C5 (SEQ ID NO: 7)(5′-TTTTCCTCA-AGCCTTCAAA-GACAG-3′) and PTEF (SEQ ID NO: 8)(5′-AGCTGCGCA-CGTCAAGACTGTCAA-GG-3′) primers were used to screen the 5′portion of the knockout construct while PBS1-2-C2 (SEQ ID NO: 9)(5′-TACCGATACATAC-GTAGCCAACAC-3′) and KAN10 (SEQ ID NO: 10)(5′-TCGCTATACTGCTG-TCGATTCGATAC-3′) primers were used to screen the 3′portion of the knockout construct. Observation of a PCR product in bothscreens is indicative of a successful knockout of the AMR2 gene sinceprimers PTEF and KAN10 anneal at the 5′ and 3′ ends of the drugresistance marker sequence, respectively; and PBS1-C5 and PBS1-2-C2 arecomplimentary to sequences in the genome that flank the 5′ and 3′regions of DNA used in the knockout construct. The new (Δoch1, Δpno1,Δmnn4b, Δamr2) strain was designated PBP130.

PCR Amplification

An Eppendorf Mastercycler was used for all PCR reactions. PCR reactionscontained template DNA, 125 μM dNTPs, 0.2 μM each of forward and reverseprimer, Ex Taq polymerase buffer (Takara Bio Inc.), and Ex Taqpolymerase (Takara Bio Inc.). The DNA fragments 5′ to the predicted AMR2gene, 3′ to the predicted AMR2 gene, and the drug resistance marker wereamplified with 30 cycles of 10 sec at 98° C., 10 sec at 52° C. and 2 minat 72° C. with an initial denaturation step of 2 min at 94° C. and afinal extension step of 10 min at 72° C. PCR samples were separated byagarose gel electrophoresis and the DNA bands were extracted andpurified using a Gel Extraction Kit from Qiagen. All DNA purificationswere eluted in 10 mM Tris, pH 8.0.

Searches and Alignments

A BLAST search to obtain sequences from completed and incomplete fungalgenomes at NCBI, was carried out, leading to the identification of AMR2homologs as discussed in the Details of the Invention. The alignmentshown in FIG. 5 was constructed using the Megalign program (DNAStar) andClustalW algorithm.

Example 4 Determination of α-Mannosidase Resistant N-Glycans in P.pastoris

N-linked glycans in YAS137 and PBP 130 were analyzed by secreting aHis-tagged reporter protein expressed under the control of the methanolinducible AOX1 promoter. The reporter protein, K3, contains a singleN-linked glycosylation site. Briefly, a shake flask containing BMGY wasinoculated with a fresh culture of YAS-130 and grown to an O.D. of ˜20.The culture was centrifuged and the cell pellet washed with BMMY(buffered minimal methanol: same as BMGY except 0.5% methanol instead of1% glycerol). The cell pellet was resuspended in BMMY to a volume ⅕ ofthe original BMGY culture and placed in a shaker for 24 h. The secretedprotein was harvested by pelleting the biomass by centrifugation andtransferring the culture medium to a fresh tube. The His-tagged K3protein was then purified on a Ni-affinity column and digested withPNGase (Choi et al., 2003).

Example 5 Analysis of Man10 and Man11/12

Structural analysis of the glycans recalcitrant to α-mannosidasedigestion disclosed at least one β1,2-mannosyl residue linked to a coremannose oligosaccharide. Structure I shows a proposed β-mannosyl residue13 shown on branch 5, which can be definitively linked to that chain,and is likely to be an integral part of the high-mannose structure. Theresidues on the following glycan structure (Structure I) was numberedbased on the paper by Ziegler et al, (Ziegler, F. D., J. Cavanagh, C.Lubowski, R. B. Trimble, 1999, Glycobiology 9:497-505), with additionalnumbers (13,14,15) added arbitrarily.

Data from three samples were analyzed for the presence of β-mannosylresidues.

Sample 1: “man10”—this was the original sample described as a man9/10mixture

Sample 2: “man11”—this was a second preparation described as man11/man12mixture from P4 fractions 63-66 with estimated 50% man11, 15% man12.

Sample3: “man10_digest”—this was a third preparation wherein theoriginal man11/man12 mixture was treated with α1,2—mannosidase to trimback to man9 or man10.

A fourth sample containing the core man8/man9 mixture was also examined.

Samples were lyophilized from D2O, and redissolved into 200 uL or 500 uLD2O. NMR data were collected on Varian Inova 600 MHz and 800 MHzspectrometers at 25 C.

Standard experiments from the Varian library (gradient COSY, TOCSY,NOESY, gradient HSQC and HMBC) were used for characterization.

Evidence for β-Mannosyl Residues:

All three samples have NMR signals that are consistent with β-anomers.Three spectral features support this argument: chemical shifts, H1-H2scalar coupling, and intra-molecular NOE measurements.

Proton Chemical Shifts.

The chemical shift values of the anomeric protons for α-mannosylresidues are typically greater than 5.0 ppm, whereas the β-mannosylresidues are usually less than 5.0 ppm. There are exceptions, such asα-mannosyl residues 3, 4 and 12, so this alone does not prove anomericconfiguration.

Analysis showing the anomeric region of proton 1D spectra of the foursamples, revealed two peaks 13 and 13t, which correspond to a α-mannosylresidue linked 1-2 to 11, where 13t is a terminal residue, and 13 seemsfurther substituted with an α-mannosyl residue 14. One can compare thesespectra to NMR data from high-mannose structures found in Ziegler etal., which show only the core residues 3 and 4, and the residue 12, inthe chemical shift region below 5 ppm.

Additional chemical shifts were extracted from the 2D TOCSY data, whichshows distinct H1,H2,H3,H4 and H5 signals from residue 13 whichcorrespond closely to data reported in Trinel et al, JBC 1999 and Nitzet al, JBC 2002. The signals from the terminal residue 13t are not aswell separated but have similar shifts (see Table 1).

The 2D TOCSY (a proton-proton correlated map) showed crosspeaksbelonging to the β-Man 13 residue (data not shown). Chemical shifts ofβ-mannosyl residues and the literature values are listed in Table 1.

TABLE 1 H1 H2 H3 H4 H5 β-man 13 4.90 4.35 3.75 3.64 3.40 β-man 13t 4.864.27 3.67 3.47 3.40 Trinel et at. 4.90-5.05 4.16-4.41 3.63-3.733.47-3.59 3.41 Nitz et at. 4.95 4.42 3.62 3.56 Chemical shifts fora-Mannosyl residues have generally the same order, but the values for H2are typically ~0.1 ppm lower, H3 are ~0.1 ppm higher and H5 are ~0.2 ppmhigher. (Trinel, P.-A., Y. Plancke, P. Gerold, T. Jouault, F. Delplace,R. T. Schwarz, G. Strecker, and D. Poulain, 1999, J.Biol.Chem. 274:30520-30526) (Nitze. M, C.-C. Ling, A. Otter, J. E. Cutler, D. R.Bundle, 2002, J.Biol.Chem., 277: 3440-3446)NOE Crosspeaks.

The β-anomeric proton is on the same face of the pyranose ring as the H3and H5 and about 2.4 Angstroms apart, whereas the α-anomeric proton ison the opposite face, and closer to 4 Ang. from either H3 or H5.Therefore, one expects a strong NOE signal between H1 and H3 and H5 inthe β-anomer. This is clearly shown in the NOESY data (not shown), wherethe spectrum shows the NOE crosspeaks that arise from through spaceinteractions and are highly distance dependent. The horizontal line at4.895 ppm corresponds to the H1 of the β-man 13 residue (data notshown). The vertical lines confirm the assignment of these peaks tospecific resonances, as determined by the TOCSY experiment in the toppanel. The strong peaks H3 and H5 are due to intra-residue NOEs betweenH1 and H3 or H5, confirming the β-anomeric assignment (data not shown).

H1 to H2 Scalar Coupling (‘Splitting’ of Peaks)

The magnitude of the proton scalar coupling that gives rise to‘splittings’ of resonances and multiplet structure is related to therelative orientation of the protons involved. It can thus be anindication of anomeric configuration.

The H1-H2 scalar coupling in α-mannosyl residues is about 1.5 Hz,whereas the β-anomer is <1 Hz. In spectra with very narrow lines you cansee the splitting for the α-anomer, whereas the β-anomer is too smalland the signals look like singlets. In these data, the linewidth was notoptimal, so both sets of peaks look like singlets. However, the patternand intensity of peaks in the 2D TOCSY (data not shown) is alsodependent on the magnitude of the coupling. A region from the TOCSYspectrum shows where the horizontal lines correspond to H1 signals, andthe crosspeaks are from other protons in the respective residues. Firstthe peaks in the H2 region that are linked to β-Man residues (3,13,13t)are lower intensity than the α-Man peaks (e.g. 4). The intensity is arough indication of the efficiency of the signal transfer and thereforethe size of the coupling constant.

The α-anomers also show additional crosspeaks from H1 to H3 andsometimes H4-this means that the scalar coupling between H1 and H2 issufficiently large to allow transfer of the signal beyond H2. Theβ-anomers, on the other hand, show only H1 to H2 crosspeaks; since thecoupling is so small the transfer of signal is very inefficient anddoesn't continue to other protons in the ring. The patterns for 13, 13tand 3 are the same, but clearly different from the other mannosylresidues.

Evidence for Linkage Position of β-Mannosyl 13(t).

Changes in H1 and H2 Chemical Shifts.

For a known high-mannose structure, it is usually sufficient to comparethe H1 and H2 proton chemical shifts with standard literature values toarrive at a structure. In this case, anomalous signals required moreeffort to establish linkages. However, there were some peaks that couldbe assigned to the core structure, such as shown for the Man8/9spectrum. Comparing the Man8/9 and the Man9/10 spectra (data not shown),there are many differences, including the new signals 13 and 13t, whichhave been described above as β-mannosyl residues.

Comparing the spectra of samples Man9/10 and Man11/12, the terminalα-mannosyl residues similar to 9 have returned. This would suggest thepeak labeled 6,12 in the Man9/10 spectrum is likely to be terminal 6,since it is expected to shift upon substitution with another α-mannose.It returns to the original position in the mannosidase digested sample,Man 10-digest. The carbon-proton correlated data (HSQC, HMBC spectra notshown) from the Man11, and Man 10-digest samples confirms that thisresidue is connected in a 1-6 linkage.

The signal labeled 14, is proposed to be an α-mannosyl residue linked to13, rather than a substituted mannosyl residue 7, as is seen in typicalMan9 structures. This is based on the NOE data discussed below. However,to account for the chemical shift of the anomeric proton, it is probablyfurther substituted.

Analysis of NOE Data.

The primary data for determining linkage sites are from NOE spectra,which indicates protons that are close in space. Therefore, in additionto intra-residue NOE crosspeaks, one can also observe inter-residuecrosspeaks, which usually indicate the linkage position. In the case ofMan(1-2) linkages, one observes crosspeaks between H1 and H2 in the sameresidue, between H1 and H2 of the glycosidically linked residue, andoften between H1 and H1 of the glycosidically linked residue.

Regions from the NOESY and TOCSY spectrum of the man10 sample wereanalyzed (data not shown). In the top panel, the peaks represent thecorrelation between H1 and H2 of the identified mannosyl residues. Inthe middle panel, the signal labeled 11 shows an NOE correlation (box)between H1 and H2 of mannosyl residue 8, consistent with its assignment.If we examine the NOE crosspeaks from the anomeric protons of residues13 and 13t, there are correlations with H2 of mannosyl residue 11. Thislinks the β-mannosyl residues to the 1-3 branch of the coreoligosaccharide. The lower panel shows an additional strong NOEcorrelation between H1 of 13t and H1 of 11, also consistent with aβ(1-2) linkage.

Additional support for this structural fragment comes from the unusualchemical shift of the H2 of mannosyl residue 11; its value is consistentwith data from Trimble et al (Trimble, R. B., C. Lubowski, C. Hauer III,R. Stack, L. McNaughton, T. Gemmill, and S. Anand Kumar, 2004,Glycobiology 14:265-274)) showing chemical shifts of 4.26 ppm forα-mannosyl residues 2-substituted by β-man. In addition, proton-carboncorrelated data (HSQC and HMBC spectra, not shown) indicate that thecarbon chemical shifts of the C2 of mannosyl 11 (as well as 8 and 5, forexample) are at high values (˜82-84 ppm) characteristic of carbons inglycosidic linkages.

We conclude that at least one β-mannosyl residue can be shown to belinked 1-2 to a core mannose oligosaccharide. There may be multiplelinkage sites for the β-mannosyl residues, and they themselves may besubstituted.

REFERENCES

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1. A modified Pichia pastoris host cell characterized in that the hostcell has been modified to reduce or eliminate expression of a functionalgene product of a nucleic acid sequence encoding a polypeptide havingthe amino acid sequence set forth in SEQ ID NO:12 and of one or morenucleic acids encoding at least one polypeptide having an amino acidsequence selected the group consisting of SEQ ID NO:13, SEQ ID NO:14,and SEQ ID NO:15.
 2. The modified host cell of claim 1 wherein thenucleic acid sequences are disrupted or deleted.
 3. The modified hostcell of claim 1 wherein expression has been reduced or eliminated forthe functional gene products encoded by SEQ ID NO:12, SEQ ID NO:13, SEQID NO:14, and SEQ ID NO:15.
 4. The modified host cell of claim 2 whereinthe disruption or deletion eliminates β-mannosylation of N-glycans. 5.The host cell of claim 1, wherein the host cell further comprisesdeletion of a functional gene product encoding an alpha-1,6mannosyltransferase activity.
 6. The host cell of claim 1, wherein thehost cell further comprises deletion of a functional gene productencoding mannosylphosphate transferase activity.
 7. A method forproducing glycoprotein compositions in Pichia pastoris host cells, saidglycoprotein compositions having reduced amounts of high mannoseglycans, said method comprising reducing or eliminating expression of afunctional gene product of a nucleic acid sequence encoding apolypeptide having the amino acid sequence set forth in SEQ ID NO:12 andof one or more nucleic acids encoding at least one polypeptide having anamino acid sequence selected the group consisting of SEQ ID NO:13, SEQID NO:14, and SEQ ID NO:15.
 8. The modified host cell of claim 7 whereinthe nucleic acid sequences are disrupted or deleted.
 9. The modifiedhost cell of claim 7 wherein expression has been reduced or eliminatedfor the functional gene products encoded by SEQ ID NO:12, SEQ ID NO:13,SEQ ID NO: 14, and SEQ ID NO:
 15. 10. The modified host cell of claim 8wherein the disruption or deletion reduces or eliminates β-mannosylationof N-glycans.
 11. The host cell of claim 7, wherein the host cellfurther comprises deletion of a functional gene product encoding analpha-1,6-mannosyltransferase activity.
 12. The host cell of claim 7,wherein the host cell further comprises deletion of a functional geneproduct encoding mannosylphosphate transferase activity.